With its development, the inkjet printing technology has been widely used in various industries. Also a variety of substrates of different materials are being printed on, such as display boards, glasses, tiles, shells of the cell phone, leather products, etc. Usually, the substrates have indent (depression) or emboss (extrasion) of different Z axis height that is defined as uneven Z height surface elevation features, the position of which need to be printed by inkjet printing. In this case, the control system will control the print heads to start printing from the one side of the elevation contours to the other side, so as to make the image or character printed overlap with the contour of the uneven Z height surface elevation features. The existing inkjet printing first performs printing test on the objects and then adjust the position parameters according to the test result, until the position meets the requirement. Using this method, if the print objects are changed, the printing test, position parameter adjustment must be redone, because the position of the uneven Z height surface elevation features are changed. Due to the irregularity of the distribution of the elevation contours or frequent change of the print objects, testing and adjustment will be quite cumbersome.
Sometimes, not only the contours of uneven Z height surface elevation features need to be printed, but also the full coverage pixel points composing the uneven Z height surface elevation features should be printed with image or characters. Under this situation, the image processing program and the recognizing procedure will be more complex.
If the uneven Z height surface elevation features on the object to be printed have color difference, the image processing method can be used to position the different colors, find the position at which the print heads should print and timely print the image or character at this position. If there is no color difference on the uneven Z height surface elevation contours, only using the light and shade changed which reflected by the indent (depression) or emboss (extrasion) to distinguish the elevation contours will cause printing position inaccuracy.